This invention relates generally to methods for making plastic containers, cosmetic compacts and the like, and more particularly to methods of providing a hinge construction between two mating casing enclosures or halves, and methods of securing insert members such as mirrors in such casing halves.
In the past, there have been proposed a number of schemes for molding plastic containers or casings of the kind employed in cosmetic compacts. Generally, the casings heretofore produced consisted of two mating casing parts or halves, each of which was molded separately. The molds incorporated recessed portions that formed halves of a hinge, each hinge half being adapted to mate with the corresponding second hinge half.
Several drawbacks became apparent with this construction. In most circumstances, the hinges required separate and distinct hinge pins to effect assembly of the casing halves. Such pins were usually constituted of metal and necessitated an additional step during the assembly of the finished case. In addition, problems with misalignment could occur, and there sometimes developed a tendency for the pin to fall out. Breakage of the plastic hinge halves sometimes occurred as the hinge pins were being press-fitted therein. At best, these prior constructions were costly and actually represented a compromise in that additional assembly time was always involved.
As a further example, in cosmetic compacts, mirror members were disposed in one of the casing halves and were usually retained in place either by a press fit, or by ultrasonic welding, glue, or cement; alternately, a separate retainer ring or bezel was employed, which latter was received in an undercut surface of an annular portion or recess of the compact.
There were several disadvantages to the above arrangements. Press-fitting was not satisfactory, since it imposed stringent requirements in the form of tolerances of the mirror and of the recess in which the mirror was to be received. Glues and cements on the other hand were messy and time-consuming to use. Also, care had to be taken not to let the solvent of the glue contact the silvered surface of the mirror. Retainer rings or bezels represented workable solutions to the problem of securing a mirror in place, but such rings resulted in additional expense, inasmuch as they constituted separate parts that had to be molded to fairly close tolerances, and since they required additional assembly time.